1. Field of the Invention
The present invention relates to exposure apparatuses and device manufacturing methods, and more particularly to an exposure apparatus that exposes an object with an energy beam via an optical system, and a device manufacturing method that uses the exposure apparatus.
2. Description of the Background Art
Conventionally, in a lithography process for manufacturing electron devices (microdevices) such as semiconductor devices (integrated circuits or the like) or liquid crystal display elements, an exposure apparatus such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper), or a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner)) is mainly used. This type of the projection exposure apparatus has a stage device that holds a substrate such as a wafer or a glass plate (hereinafter, generically referred to as a wafer) and drives the wafer along a predetermined two-dimensional plane.
In order to perform high-precision exposure, the high-precision positional controllability of a stage is required for the stage device, and in order to improve throughput of the exposure operation, higher speed and higher acceleration of the stage are also required. To cope with these requirements, in recent years, a stage device that controls the position of a wafer within a two-dimensional plane using a planar motor by an electromagnetic force drive method has been developed (e.g. refer to U.S. Pat. No. 6,437,463).
Further, for example, the fifth embodiment of U.S. Patent Application Publication No. 2008/0094594 discloses the exposure apparatus in which an encoder head is placed within a recessed section formed on the upper surface of a surface plate. In the exposure apparatus described in U.S. Patent Application Publication No. 2008/0094594, positional information of the wafer stage is measured with high precision by causing measurement beams to be incident on a two-dimensional grating placed on the wafer stage from directly below.
However, if the planar motor in which the wafer stage has the mover and the surface plate has the stator as disclosed in U.S. Pat. No. 6,437,463 is applied to the exposure apparatus in which the encoder head is placed inside the surface plate as disclosed in the fifth embodiment of U.S. Patent Application Publication No. 2008/0094594, there is a possibility that the measurement accuracy of the encoder system is degraded owing to a reaction force acting on the surface plate when the wafer stage is driven.